Organic Management of Diamondback Moth and Similar Insects

fresh cabbage

The diamondback moth is one of several species of moths and butterflies whose larvae feed on cabbage and related crucifers in New York. Plans to test a genetically engineered diamondback moth at the NY Agriculture Experiment Station in Geneva NY have been in the news recently. The genetically engineered diamondback moth was developed in England by Oxitec.

Researchers are studying if the introduction of the genetically engineered diamondback moths into fields where diamondback moths are naturally present is a way to reduce crop damage due to diamondback moth larvae. Caged trials of genetically engineered diamondback are being done and open field trials have been proposed. The proposed trials, especially the open field trials are controversial. There are many questions regarding the risks associated with releasing genetically engineered insects into the environment. Many people believe more needs to be learned about the potential impacts of releasing the genetically engineered moths before open field trials are conducted.

Organic growers – both small and commercial scale – have many tools in the toolbox to control these insects and limit the damage caused by the insect. In fact, organic and IPM methods when properly timed and used appropriately will do an excellent job in managing diamondback moth.

The most effective organic control methods rely on exclusion, like insect netting or row cover, or timely and regular treatment to ensure that populations do not increase. An IPM approach where sprays or other applications of materials are made once a threshold population level is observed is often effective. At low population levels, naturally occurring insects and parasitoids may be sufficient to control diamondback moth populations. Heavy rainfall has been observed to reduce larva and even well timed use of sprinklers simulating a heavy rainfall can reduce larval populations.

Where the crop is in its growth cycle also needs to be considered as the risk of significant crop damage changes as the crop grows. So, while it may make sense to treat a young crop if diamondback moth larvae are found in 10% of the crop or a certain number are found on a sticky trap placed in the field, later in the season, the threshold might be 30% or more before taking action.

Several varieties of parasitic wasps and flies have also been found to be effective. In addition, several OMRI approved materials have been found to work well if spraying is needed. Entrust and Dipel DF are both effective against diamondback moth and other larvae which could be present on the affected crop. These materials are also very specific and affect larvae feeding on the crop, but do not kill the beneficial insects which feed on the larvae. Pyganic is also labeled for diamondback larvae, imported cabbageworms and several other larvae which may feed on cabbage and related crops, but is a broad spectrum insecticide and will also kill many of the beneficials feeding upon the larvae.

Diamondback moth is not the only insect whose larvae feed on cabbage and related crucifers. In NY, cabbage loopers, imported cabbageworms and cabbage moths also have similar life cycles and feeding preferences. Organic control methods for these pests are similar. The life cycle for these pests is short, with several generations occurring each season. Several species may be present at any time in the field and with early prevention and monitoring, they can be successfully controlled using organic methods.

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